Rod-like Architecture Research Articles

Rod-like architecture and cross-sectional structure of an amyloid protofilament-like peptide supermolecule in aqueous solution

A β-sheet-forming peptide conjugated with a water-soluble moiety (polyethylene glycol (PEG) or a transactivator of transcription (TAT) sequence) forms rod-like aggregates in aqueous solution. We explored the detailed structures of the aggregates using Synchrotron X-ray scattering. We found that the β-sheet-forming peptide indeed formed stacked β-sheets, in a manner similar to that observed in the case of amyloid protofilaments. We also found that the resultant rod-like objects could be completely dispersed in water, as a result of the hydrophilicity of PEG or TAT.

Synthesis of SiC decorated carbonaceous nanorods and its hierarchical composites Si@SiC@C for high-performance lithium ion batteries

SiC- based nanomaterials possess superior electric, thermal and mechanical properties. However, due to the tricky synthesis process, which needs to be carried out under high temperature with multi-step reaction procedures, the further application is dramatically limited. Herein, a simple as well as a controllable approach is proposed for synthesis of SiC- based nanostructures under low temperature. Phenyl-bridged polysilsesquioxane was chosen as the starting material to react with magnesium at 650 °C, following which SiC@C nanocomposites were finally obtained, and it maintains the original bent rod-like architecture of polysilsesquioxanes. The possible formation process for the nanocomposites can proposed as well. The electrochemical behaviour of nanocomposites was accessed, verifying that the synthesized SiC@C nanocomposites deliver good electrochemical performance. Moreover, SiC@C also shows to be a promising scaffold in supporting Si thin film electrode in achieving stable cycling performance in lithium ion batteries.

Growth of Variable Aspect Ratio ZnO Nanorods by Solochemical Processing

In this work, variable aspect ratio (length divided by diameter) zinc oxide nanorods were synthesized through a simple solochemical method by reacting a Zn2+ precursor with sodium hydroxide at low reaction temperatures. The analysis of the X-ray diffraction data indicated that the samples had hexagonal wurtzite structure and nanometric size crystallites. The transmission electron microscopy (TEM) images of the products prepared at 60 and 80 °C exhibited rod-like architecture, showing that the reaction temperature did not affect the ZnO morphology. The average aspect ratio of the ZnO nanorods decreased from 3.4 to 2.4 when the reaction temperature was raised from 60 to 80 °C. The samples presented a blue shift in the excitonic absorption compared to ZnO bulk that increased alongside with reaction temperature. In addition, this research investigated the results obtained by varying the concentration of zinc chloride solution. At the same temperature, it could be verified that when the zinc concentration was increased, the diameter of the ZnO nanorods also slightly increased, and much shorter nanorods were achieved, especially in the reactions performed at 50 and 70 °C. Finally, the growth mechanism of the ZnO nanostructures was proposed based on the results obtained by changing the zinc precursor concentration and reaction temperature.

Structural insights into SraP-mediated S. aureus adhesion to host cells

Staphylococcus aureus, a Gram-positive bacterium causes a number of devastating human diseases, such as infective endocarditis, osteomyelitis, septic arthritis and sepsis. S. aureus SraP, a surface-exposed serine-rich repeat glycoprotein (SRRP), is required for the pathogenesis of human infective endocarditis via its ligand-binding region (BR) adhering to human platelet. It remains unclear how SraP interacts with human host. Here we report the 2.05 Å crystal structure of the BR of SraP, revealing an extended rod-like architecture of four discrete modules. The N-terminal legume lectin-like module specifically binds to N-acetylneuraminic acid. The second module adopts a β-grasp fold similar to Ig-binding proteins, whereas the last two tandem repetitive modules resemble eukaryotic cadherins but differing in calcium coordination pattern. Small-angle X-ray scattering and molecular dynamic simulation indicated the three C-terminal modules function as a rigid stem to extend the N-terminal lectin module outward. Further structure-guided mutagenesis analyses showed that SraP binding to sialylated receptors promotes S. aureus adhesion to and invasion into host epithelial cells. Our findings have thus provided novel structural and functional insights into the SraP-mediated interaction of S. aureus with host epithelial cells.

Structural insights into SraP-mediated Staphylococcus aureus adhesion to host cells.

Staphylococcus aureus, a Gram-positive bacterium causes a number of devastating human diseases, such as infective endocarditis, osteomyelitis, septic arthritis and sepsis. S. aureus SraP, a surface-exposed serine-rich repeat glycoprotein (SRRP), is required for the pathogenesis of human infective endocarditis via its ligand-binding region (BR) adhering to human platelets. It remains unclear how SraP interacts with human host. Here we report the 2.05 Å crystal structure of the BR of SraP, revealing an extended rod-like architecture of four discrete modules. The N-terminal legume lectin-like module specifically binds to N-acetylneuraminic acid. The second module adopts a β-grasp fold similar to Ig-binding proteins, whereas the last two tandem repetitive modules resemble eukaryotic cadherins but differ in calcium coordination pattern. Under the conditions tested, small-angle X-ray scattering and molecular dynamic simulation indicated that the three C-terminal modules function as a relatively rigid stem to extend the N-terminal lectin module outwards. Structure-guided mutagenesis analyses, in addition to a recently identified trisaccharide ligand of SraP, enabled us to elucidate that SraP binding to sialylated receptors promotes S. aureus adhesion to and invasion into host epithelial cells. Our findings have thus provided novel structural and functional insights into the SraP-mediated host-pathogen interaction of S. aureus.

Supramolecular Linear Assemblies of Cytochrome b 562 Immobilized on a Gold Electrode

Linear assemblies of cytochrome b562 (cyt b562) containing a chemically-modified heme molecule on the protein surface were constructed by successive intermolecular heme–heme pocket interactions and then immobilized onto a gold electrode via a heme molecule anchored on the electrode. The accumulation of the cyt b562 units were confirmed by electrochemical analyses. The average number of proteins in each assembly was estimated to be about 6 units by quartz crystal microbalance and atomic force microscopy (AFM) analyses. The linear assemblies of the cyt b562 units were clearly visualized by AFM as a rod-like architecture with a vertical orientation to the electrode surface.

Interaction between polydeoxyadenylic acid and β-glucan from Lentinus edodes

The interaction between polydeoxyadenylic acid (poly(dA)) and single chains of Lentinan (s-LNT) was investigated by circular dichroism spectra (CD), UV–Vis spectra, nano-differential scanning calorimetry (nano-DSC), dynamic light scattering (DLS), and atomic force microscopy (AFM). All the experimental results indicated that poly(dA) really interacted with s-LNT having molecular weight of 5.3×105 to form a novel composite with stiff conformation through hydrogen bonding, whereas the triple helical Lentinan (t-LNT) could not, implying that it was the single chain but not the triple helical chain interacted with poly(dA). Meanwhile, the interaction strongly depended on the concentration of s-LNT and pH. When the poly(dA) concentration was fixed at 5.3μg/ml, the interaction between poly(dA) and s-LNT increased with an increase in s-LNT concentration, then reached the maximum at ∼60μg/ml, finally decreased with further increase of s-LNT concentration. This was due to self-renaturation of s-LNT into triple helix or incomplete species confirmed by nano-DSC. The poly(dA)/s-LNT complex could exist in solutions with pH 5.5–11.5, and pH 7–10 was the optimal condition for the complex, showing higher stability against pH than the positive control of poly(dA)/s-SPG. The dynamic behaviors of the complex demonstrated that the interaction between s-LNT and poly(dA) occurred rapidly, and reached stable within 3–7h. Moreover, the thermal stability of poly(dA) was enhanced by complexation with s-LNT. The topograph of the poly(dA)/s-LNT complex was shown as rod-like stiff architecture. This work enlarges the application of LNT in the biomedical field.

Age-related changes in human trabecular bone: Relationship between microstructural stress and strain and damage morphology

Accumulation of microdamage in aging and disease can cause skeletal fragility and is one of several factors contributing to osteoporotic fractures. To better understand the role of microdamage in fragility fracture, the mechanisms of bone failure must be elucidated on a tissue-level scale where interactions between bone matrix properties, the local biomechanical environment, and bone architecture are concurrently examined for their contributions to microdamage formation. A technique combining histological damage assessment of individual trabeculae with linear finite element solutions of trabecular von Mises and principal stress and strain was used to compare the damage initiation threshold between pre-menopausal (32–37 years, n=3 donors) and post-menopausal (71–80 years, n=3 donors) femoral cadaveric bone. Strong associations between damage morphology and stress and strain parameters were observed in both groups, and an age-related decrease in undamaged trabecular von Mises stress was detected. In trabeculae from younger donors, the 95% CI for von Mises stress on undamaged regions ranged from 50.7–67.9MPa, whereas in trabeculae from older donors, stresses were significantly lower (38.7–50.2, p<0.01). Local microarchitectural analysis indicated that thinner, rod-like trabeculae oriented along the loading axis are more susceptible to severe microdamage formation in older individuals, while only rod-like architecture was associated with severe damage in younger individuals. This study therefore provides insight into how damage initiation and morphology relate to local trabecular microstructure and the associated stresses and strains under loading. Furthermore, by comparison of samples from pre- and post-menopausal women, the results suggest that trabeculae from younger individuals can sustain higher stresses prior to microdamage initiation.

Microarchitecture influences microdamage accumulation in human vertebral trabecular bone.

It has been suggested that accumulation of microdamage with age contributes to skeletal fragility. However, data on the age-related increase in microdamage and the association between microdamage and trabecular microarchitecture in human vertebral cancellous bone are limited. We quantified microdamage in cancellous bone from human lumbar (L2) vertebral bodies obtained from 23 donors 54–93 yr of age (8 men and 15 women). Damage was measured using histologic techniques of sequential labeling with chelating agents and was related to 3D microarchitecture, as assessed by high-resolution μCT. There were no significant differences between sexes, although women tended to have a higher microcrack density (Cr.Dn) than men. Cr.Dn increased exponentially with age (r = 0.65, p < 0.001) and was correlated with bone volume fraction (BV/TV; r = −0.55; p < 0.01), trabecular number (Tb.N; r = −0.56 p = 0.008), structure model index (SMI; r = 0.59; p = 0.005), and trabecular separation (Tb.Sp; r = 0.59; p < 0.009). All architecture parameters were strongly correlated with each other and with BV/TV. Stepwise regression showed that SMI was the best predictor of microdamage, explaining 35% of the variance in Cr.Dn and 20% of the variance in diffuse damage accumulation. In addition, microcrack length was significantly greater in the highest versus lowest tertiles of SMI. In conclusion, in human vertebral cancellous bone, microdamage increases with age and is associated with low BV/TV and a rod-like trabecular architecture.

Rod-like architecture and helicity of the poly(C)/schizophyllan complex observed by AFM and SEM

Microscopic studies of the complex between poly(C) and schizophyllan (SPG), employing both AFM and SEM, revealed that the complex takes the same rod-like architecture on the mica surface as those of the renatured SPG and the original triple helix of SPG, indicating that the complex also has a helical structure. The SEM observations showed the helical pattern on the rod surface, only when the sample was metal shadowed. The pitch evaluated from the image is comparable with that obtained from crystallographic data. The ability to visualize the helical structure can be explained from the hypothesis that the platinum grains may assemble on the sample using the molecular surface of the SPG (or complex) as the template.

Morphological Characterization of the Molecular Superstructure of Polyphenylene Ethynylene Derivatives

Two different polyphenylene ethynylene derivatives, one partly hydrophobic and one hydrophilic, were investigated with a combination of X-ray and light scattering techniques and hydrodynamic techniques, as well as scanning force microscopy and transmission electron microscopy to elucidate their molecular structure and aggregation behavior in tetrahydrofuran and water, respectively. It turns out that both polymers possess a rod-like molecular architecture which, however, is the basis of a cascade of aggregation steps. Both, electron microscopy and X-ray analysis support the concept of a primary back-to-back aggregation of polymer chains into cylindrically shaped aggregates with high anisometry. The thickness of these aggregates was between 4.0 and 4.5 nm. The aggregates of the hydrophobic polymer further associate into fibrils and these fibrils form clusters of globular shape, though with high internal anisometry.

Organotin biocides. Part 2. Variable-temperature119Sn Mössbauer study of phenyl- and cyclohexyl-tin compounds

The temperature dependence of the recoil-free fraction (a=–d In f/dT) for 13 phenyl- and 11 cyclohexyl-tin compounds has been investigated, and the results interpreted in terms of the lattice structures of the compounds. This interpretation is aided by a classification of organotin polymers based upon the stereochemical disposition of tin and the bridging groups. Lattices based upon non-interacting units, or polymers which are helical (Class 4) or ‘S’-shaped (Class 3), show the highest a values. The value of this parameter is generally reduced for zigzag (Class 2) polymers, while the most rigid lattices (lowest a) are based upon a rod-like (Class 1) architecture.